1. Field of the Invention
The present invention relates to an automatic following travel system wherein, among a plurality of queued vehicles, a leading vehicle positioned at the front is operated by an operator, and the following vehicles positioned behind the leading vehicle automatically follow the leading vehicle so as to travel in a procession.
This application is based on Japanese Patent Application Nos. 11-177530, and 11-177531, the contents of which are incorporated herein by reference.
2. Description of the Related Art
As is commonly known, systems have been proposed wherein small electric vehicles are used in common by a plurality of users in a defined region, and thereby, efficient use of the vehicles is achieved, and by means of this, problems such as congestion and insufficient space are relieved, and a saving in resources and energy, as well as a reduction of environmental contamination, are achieved.
In other words, dedicated parking area, related ports, are established at a number of places within a limited region, and users are able to freely borrow vehicles from these ports, and furthermore, after the use of the vehicles, the vehicles may be returned to the ports. By means of this, users are able to employ the vehicles only when they are required. Furthermore, if there are a large number of ports, it is not necessary to search for parking spaces or to park along the side of the road, and it is thus possible to alleviate congestion.
However, in such a system, as a result of the locations of the ports or the like, there are concerns that vehicles may become concentrated at some ports, while at other ports, vehicles will become insufficiently available.
Techniques have been proposed for moving a plurality of vehicles efficiently between ports so as to easily remedy this imbalance of vehicles between ports (for example, in Japanese Unexamined Patent Application, First Publication, No. Hei 5-170008). In this technique, among a plurality of queued vehicles, only the leading vehicle, which is positioned at the front, is manually operated by an operator, and the operation of the succeeding vehicles is automatically controlled based on data relating to the driving operations of the leading vehicle which is transmitted from the leading vehicle. By means of this, driving is controlled so that the succeeding vehicles trace the same track as the leading vehicle, and as a result, a state is realized in which a series of vehicles travel in such a manner as to form a procession with the leading vehicle in the front (processional travel). At this time, because the operation of the succeeding vehicles is automatically controlled, unmanned operation is possible, and it is possible to reduce the number of humans involved.
When traveling in a procession, each succeeding vehicle may control its accelerator, brake, and steering so as to simply trace the track of the leading vehicle. However, even when the leading vehicle and the succeeding vehicles are the same vehicle type, the coordinates for specifying the track, which are stored in the respective vehicles, may gradually come to differ from each other, depending on the road conditions, the difference in traveled distance, and an error which may arise in the control of the travel by the sensors. However accurate the control for tracing the track of the leading vehicle is made, there is the problem that the real travel tracks may be different between the leading vehicle and the succeeding vehicles because of differences in coordinates.
To solve this problem, techniques have been proposed for controlling all the vehicles to travel according to the same coordinate system. This technique comprises: calculating the difference in the coordinates, based on the track information of the leading vehicle, which is obtained by communication between the vehicles (hereinafter referred to as vehicle-to-vehicle communication), and on the radar information obtained by an object vehicle; and transforming the track (position) information of the object vehicle to the track information in the coordinate system set in the leading vehicle.
Next is a description of the technique for transforming the track information of the succeeding vehicle to the track information in the coordinate system set in the leading vehicle.
The leading vehicle and the succeeding vehicles are electric vehicles 1 shown in FIG. 8. Electric energy from a battery 2 is supplied to a motor 4 controlled by a power train ECU 3, and the motor 4 rotates wheels 5 to drive the vehicle.
As shown in FIG. 8, the electric vehicle 1 is fitted with a laser radar 6 in the center of the front bumper capable of wide angle scanning, and a reflector 7 in the center of the rear bumper, which is a plate with a mirror finish for reflecting the radar waves emitted by a laser radar 6 of a succeeding vehicle.
When the electric vehicle 1 travels, the succeeding vehicle can pick up the location of the reflector 7 of the preceding vehicle in real time using the laser radar 6 of the succeeding vehicle, and can therefore detect the location of the preceding vehicle (the distance from the preceding vehicle) and its direction in real time.
The electric vehicle 1 has a speed sensor and a yaw rate sensor, which are not shown, and recognizes its traveling direction and track in the coordinate system set in the electric vehicle.
A vehicle to vehicle antenna 8 for radio communication between the electric vehicles 1 (vehicle to vehicle communication) is installed in the roof of the electric vehicle 1. The respective vehicles can recognize the positions and tracks of the other vehicles by vehicle-to-vehicle communication using the vehicle-to-vehicle antenna 8 (the positions and tracks of the other vehicles in the coordinate systems stored in the respective vehicles). The coordinate systems in the respective vehicles are initialized so that the origins are set to a specified port for the electric vehicles 1.
In FIG. 9, two electric vehicles 1 travel as the leading vehicle 1' and the succeeding vehicle 1". In FIG. 9,
fB is the distance from the center of gravity G2 of the succeeding vehicle 1" to the laser radar 6 which is the laser measurement point,
bF is the distance from the center of gravity G1 of the leading vehicle 1' to the reflector 7,
Lx(t1) is the component in the traveling direction of the succeeding vehicle 1" between the laser radar 6 of the succeeding vehicle 1" and the reflector 7 of the leading vehicle 1' at a time t1, and
Ly(t1) is the component in the direction perpendicular to the traveling direction of the succeeding vehicle 1" between the laser radar 6 of the succeeding vehicle 1" and the reflector 7 of the leading vehicle 1' at the time t1.
Further, reference characters are defined as follows:
GF is the coordinate system of the leading vehicle,
GB is the coordinate system of the succeeding vehicle,
XF(t1) is the X-coordinate of the center of gravity of the leading vehicle 1' in the GF coordinate system at the time t1,
YF(t1) is the Y-coordinate of the center of gravity of the leading vehicle 1' in the GF coordinate system at the time t1,
.theta.F(t1) is the yaw angle of the leading vehicle 1' in the GF coordinate system at the time t1,
XB(t1) is the X-coordinate of the center of gravity of the succeeding vehicle 1" in the GB coordinate system at the time t1,
YB(t1) is the Y-coordinate of the center of gravity of the succeeding vehicle 1" in the GB coordinate system at the time t1, and
.theta.B(t1) is the yaw angle of the succeeding vehicle 1" in the GB coordinate system at the time t1.
The coordinates {X'F(t1), Y'F(t1)} of the radar measurement point (reflector 7) of the leading vehicle 1' in the GF coordinate system at the time t1 are given by: EQU X'F(t1)=XF(t1)-bF.times.cos .theta.F(t1), EQU Y'F(t1)=YF(t1)-bF.times.cos .theta.F(t1).
Similarly, the coordinates {X'FB(t1), Y'FB(t1)} of the laser measurement point (reflector 7) of the leading vehicle 1' in the GB coordinate system at the time t1 are given by: EQU X'FB(t1)=XB(t1)+{Lx(t1)+fB}.times.cos .theta.B(t1)-Ly(t1).times.sin .theta.B(t1), EQU Y'FB(t1)=YB(t1)+{Lx(t1)+fB}.times.sin .theta.B(t1)+Ly(t1).times.cos .theta.B(t1).
Further, the coordinates {X'F(t2), Y'F(t2)} in the GF coordinate system and {X'FB(t2), Y'FB(t2)} in the GB coordinate system of the radar measurement point (reflector 7) of the leading vehicle 1' at the time 2 after a predetermined time has passed from the time t1 (see FIG. 10) are given by: EQU X'F(t2)=XF(t2)-bF.times.cos .theta.F(t2),
Y'F(t2)=YF(t2)-bF.times.cos .theta.F(t2), EQU X'FB(t2)+XB(t2)+{Lx(t2)+fB}.times.cos .theta.B(t2)-Ly(t2).times.sin .theta.B(t2), EQU Y'FB(t2)=YF(t2)+{Lx(t2)+fB}.times.sin .theta.B(t2)+Ly(t2).times.cos .theta.B(t2)
As shown in FIG. 10, when the position A of the radar measurement point (reflector 7) of the leading vehicle 1' at the time t1 is connected to the position B at the time t2 by the straight line L, the coordinates of the position A in the GF coordinate system are {X'F(t1), Y'F(t1)}, and the coordinates of the position B in the GF coordinate system are {X'F(t2), Y'F(t2)}. Accordingly, the angle .theta.'F(t1, t2) between the straight line L and the XF-axis is given by: EQU .theta.'F(t1, t2)=arc tan [{X'F(t2)-X'F(t1)}/{Y'F(t2)-Y'F(t1)}.
Similarly, when the straight line L is placed in the GB coordinate system, the coordinates of the position A (see FIG. 10) are {X'FB(t1), Y'FB(t1)}, and the coordinates of the position B are {X'FB(t2), Y'FB(t2)}. Accordingly, the angle .theta.'FB(t1, t2) between the straight line L and the XB-axis is given by: EQU .theta.'FB(t1, t2)=arc tan [{X'FB(t2)-X'FB(t1)}/{Y'FB(t2)-Y'FB(t1)}].
Since in two coordinate systems the straight line L is identical, the rotation angle .DELTA..theta.FB of the GF coordinate system with respect to the GB coordinate system is given by: EQU .DELTA..theta.FB=.theta.'FB(t1, t2)-.theta.'F(t1, t2).
Further, when the position X-coordinate of the origin of the GF coordinate system with respect to the GB coordinate system is .DELTA.XFB, and the position Y coordinate of the origin of the GF coordinate system with respect to the GB coordinate system is .DELTA.YFB, the .DELTA.XFB and the .DELTA.YFB are given by: EQU .DELTA.XFB=X'FB(t2)-X'F(t2).times.cos .DELTA..theta.FB-Y'F(t2).times.sin .DELTA..theta.FB, EQU .DELTA.YFB=Y'FB(t2)-X'F(t2).times.sin .DELTA..theta.FB-Y'F(t2).times.cos .DELTA..theta.FB
As described above, the difference (deviation) {.DELTA.XFB, .DELTA.YFB, .DELTA..theta.FB} between the coordinate systems of the leading vehicle 1' and of the succeeding vehicle 1" can be expressed by the position coordinates (XF, YF, .theta.F) of the leading vehicle 1' in the coordinate system set in the leading vehicle 1', the position coordinates (XB, YB, .theta.B) of the succeeding vehicle 1" in the coordinate system set in the succeeding vehicle 1", and the laser information Lx and Ly. Thus, the succeeding vehicle 1" calculates the difference between the coordinate systems of the leading vehicle 1' and the succeeding vehicle 1" from the position and the traveling direction of the succeeding vehicle in the coordinate system set in the succeeding vehicle, the position of the leading vehicle 1' in the coordinate system set in the leading vehicle 1', and the distance and direction of the leading vehicle 1' detected by the laser radar 6. By adding the difference to the track information of the succeeding vehicle 1", the track information of the succeeding vehicle 1" can be transformed to the track information in the coordinate system set in the leading vehicle 1'.
In the above-described example, the leading vehicle 1' is single, and the succeeding vehicle 1" is single. Even when there are two or more succeeding vehicles 1" each vehicle can calculate the difference between the coordinate system set in the vehicle just in front and the coordinate system set in the vehicle itself. By calculating the differences between the coordinate systems from the leading vehicle 1' in due order, the differences between the coordinate systems of the leading vehicle 1' and the respective succeeding vehicles 1" can be calculated. Using the calculated differences, the respective succeeding vehicles 1" can transform their track (position) information to the track information in the coordinate system set in the leading vehicle 1'.
According to the above-described technique, the difference between the coordinate systems can be directly calculated only between the vehicle and the vehicle just in front of that vehicle. Therefore, when there are a certain number "n" of vehicles in front of the succeeding vehicle 1", the number of the differences which can be directly calculated is "n".
FIG. 11 schematically shows the processional travel of four electric vehicles 1. In this example, the differences between the coordinate systems which can be directly calculated by the above-described technique are three, which are:
1) the difference (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.2.fwdarw.1 between the coordinate systems of the leading vehicle 1' (hereinafter referred to as the first vehicle) and of the succeeding vehicle 1" (hereinafter referred to as the second vehicle) just behind the leading vehicle, PA1 2) the difference (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.3.fwdarw.2 between the coordinate systems of the second vehicle and of the succeeding vehicle (hereinafter referred to as the third vehicle) just behind the second vehicle, PA1 3) the difference (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.4.fwdarw.3 between the coordinate systems of the third vehicle and of the succeeding vehicle (hereinafter referred to as the fourth vehicle) just behind the third vehicle, PA1 where (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.m.fwdarw.n is a difference (x-direction, y-direction, rotation) between the coordinate systems of the M-vehicle and the N-vehicle. PA1 1) the "n"-th vehicle position information in the "n"-th vehicle coordinate system: (X.sub.n, y.sub.n, .theta..sub.n).sub.n, and, PA1 2) the "n-1"-th vehicle position information in the "n"-th vehicle coordinate system: (x.sub.n-1, y.sub.n-1, .theta..sub.n-1 t).sub.n, which are detected by the "n"-th vehicle, and PA1 3) the "n-1"-th vehicle position information in the "n"-th vehicle coordinate system: (X.sub.n-1, y.sub.n-1, .theta..sub.n-1).sub.n-1, PA1 4) the transformation by the "n-1"-th vehicle to the first vehicle coordinate system: (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.n-1.fwdarw.1, and PA1 5) the first vehicle position information in the first vehicle coordinate system: (x.sub.1, y.sub.1, .theta..sub.1).sub.1. PA1 1) the "n"-th vehicle position information in the "n"-th vehicle coordinate system: (x.sub.n, y.sub.n, .theta..sub.n).sub.n, and, PA1 2) the "n-1"-th vehicle position information in the "n"-th vehicle coordinate system: (x.sub.n-1, y.sub.n-1, .theta..sub.n-1).sub.n, which are detected by the "n"-th vehicle, and PA1 3) the "n-1"-th vehicle position information in the first vehicle coordinate system: (x.sub.n-1, y.sub.n-1, .theta..sub.n-1).sub.1, and PA1 4) the first vehicle position information in the first vehicle coordinate system: (x.sub.1, y.sub.1, .theta..sub.1).sub.1, which are obtained by vehicle-to-vehicle communication.
To obtain the difference (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.4.fwdarw.1 between the coordinate systems of the fourth vehicle and of the first vehicle, the differences 1) to 3) are added up.
To accurately calculate (.DELTA.x, .theta.y, .DELTA..theta.).sub.4.fwdarw.1, the values 1) to 3) must be calculated based on the data obtained at the same time. That is, as the differences between the coordinate systems in the respective vehicles vary every moment, in order to accurately specify the difference between the coordinate systems of the fourth vehicle and of the first vehicle at the time t, the values 1) to 3) to be included in the difference must be synchronized at the time t. That is, the difference must be based on the data obtained at the same time t. This is also true in the calculation of the difference (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.3.fwdarw.1 between the coordinate systems of the third vehicle and of the first vehicle, and in the calculation of the difference (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.n.fwdarw.1 between the coordinate systems of the first vehicle and of a n-th vehicle which is positioned behind the fourth vehicle.
To avoid the problem of the asynchrony in the data, when calculating the difference between the coordinate systems of the first vehicle and of the "n"-th vehicle according to the conventional technique, the "n"-th vehicle receives the differences, which the second, third, . . . "n-1"-th vehicles used to transform the difference between the coordinate systems, from the vehicle just in front by vehicle-to-vehicle communication, and adds these differences to the difference between the coordinate systems of the "n-1"-th vehicle and of the "n"-th vehicle. Thus, the required difference (between the coordinate systems of the first vehicle and of the "n"-th vehicle) can calculated.
Specifically, when four vehicles travel in a procession as shown in FIG. 11, the respective vehicles calculate the desired differences. In the following formulas, (xn, yn, .theta.n).sub.m is the position and traveling direction of the "n"-th vehicle expressed in the coordinate system set in the "m"-th vehicle.
To obtain the value (x2, y2, .theta.2).sub.1 of the position coordinates of the second vehicle converted into the coordinate system of the first vehicle, the second vehicle calculate:
(x2, y2, .theta.2).sub.1 =(x2, y2, .theta.2).sub.2 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.2.fwdarw.1.
By this calculation, the second vehicle can convert its coordinates into the value in the coordinate system set in the first vehicle, based only on the information obtained by the second vehicle itself (that is, the position and traveling direction in its own coordinate system, and the difference between the coordinate systems of the second vehicle and of the vehicle in front).
However, to obtain the value (x3, y3, .theta.3).sub.1 of the position coordinates of the third vehicle converted into the coordinate system of the first vehicle, the third vehicle must calculates: EQU (x3, y3, .theta.3).sub.1 =(x3, y3, .theta.3).sub.3 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.3.fwdarw.1.
Because in this calculation the value (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.3.fwdarw.1 cannot be directly calculated based on the laser information, the third vehicle adds its position and traveling direction (x3, y3, .theta.3).sub.3 in its own coordinate system to the difference (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.3.fwdarw.2 between the coordinate systems of the second vehicle and of the third vehicle, which was calculated by the third vehicle, to thereby obtain the position and traveling direction (x3, y3, .theta.3).sub.2 of the third vehicle in the coordinate system set in the second vehicle. Then, the third vehicle adds this obtained value to the difference between the coordinate systems of the second vehicle and of the first vehicle, to thereby obtain (x3, y3, .theta.3).sub.1.
That is, EQU (x3, y3, .theta.3).sub.2 =(x3, y3, .theta.3).sub.3 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.3.fwdarw.2.
Accordingly, EQU (x3, y3, .theta.3).sub.1 =(x3, y3, .theta.3).sub.2 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.2.fwdarw.1 =(x3, y3, .theta.3).sub.3 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.3.fwdarw.2 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.2.fwdarw.1.
Similarly, the value (x4, y4, .theta.4).sub.1 of the position coordinates and traveling direction of the fourth vehicle converted into the coordinate system of the first vehicle is calculated by: EQU (x4, y4, .theta.4).sub.1 =(x4, y4, .theta.4).sub.2 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.2.fwdarw.1 EQU =(x4, y4, .theta.4).sub.3 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.3.fwdarw.2 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.2.fwdarw.1 EQU =(x4, y4, .theta.4).sub.4 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.4.fwdarw.3 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.3.fwdarw.2 +(.DELTA.x, .DELTA.y, .DELTA..theta.).sub.2.fwdarw.1.
It is understood that, as the vehicle is nearing the end of the procession, the terms required for the formula for converting the position of the succeeding vehicle 1" in the coordinate system in the succeeding vehicle 1" into the value in the coordinate system of the leading vehicle 1' increase. Therefore, the load due to the calculation by the vehicles behind significantly increases.
Further, to avoid the problem of the asynchrony in data, the information regarding the differences between the coordinate systems used in the transformation should be identical to those used by the vehicles in front which have transformed their positions. When all the information is supplied from the vehicles in front by vehicle-to-vehicle communication, the information to be transmitted from the second vehicle to the third vehicle includes only (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.2.fwdarw.1, and the information to be transmitted from the second vehicle to the third vehicle must include two data points (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.2.fwdarw.1 and (.DELTA.x, .DELTA.y, .DELTA..theta.).sub.3.fwdarw.2. Further, n-1 points data must be transmitted to the "n"-th vehicle behind these vehicles. Therefore, when a number of vehicles travels in a procession, the communication buffer capacities required for the vehicle-to-vehicle communication must be increased, the loads on the CPUs in the respective vehicles are also increased, and thereby quick control may be impossible.